Walls that support load-bearing concrete block masonry buildings need to account for a variety of situations. From resisting out-of-plane and in-plane axial combinations, to fire and sound barriers, and possibly serving as an exposed architectural finish. That’s a lot for one wall to manage! And then there are the aesthetics, running bond patterns (think overlapping bricks) versus stack patterns (one brick stacked directly over another). How does this design element change the load for that wall? A lack of overlap has been observed to create planes of weakness that can be susceptible to cracking, but there has been little research to verify this, which has resulted in contradictory design requirements between the U.S. and Canada for load-bearing stack pattern masonry.
For a new study in the Journal of Structural Engineering, “Out-of-Plane Behavior of Reinforced Stack Pattern Tall Masonry Walls,” researchers compared the behaviors of running bond and stack pattern walls when subjected to both axial loads and out-of-plane bending loads. Their experiment involved construction of six full-scale masonry walls, varying by unit pattern, reinforcement size, and spacing. Learn more about the research by authors Brodie Van Boxtel, Samuel Ehikhuenmen, Sreekanta Das, and Bennett Banting and the resulting load–displacements, moment–displacements, and failure modes of their test walls at https://doi.org/10.1061/JSENDH.STENG-12943. The abstract is below.
Abstract
Load-bearing masonry is widely used in North America, offering architects various unit patterns, including running bond and stack bond, for both architectural and load-bearing purposes. However, stack pattern masonry in load-bearing walls faces additional design restrictions compared to running bonds. Many prefer stack patterns for their aesthetics but are often unaware of the structural limitations. These constraints originate from research on unreinforced or ungrouted stack pattern walls, with the misconception arising when horizontal reinforcement or continuous grouting is used. Thus, stack pattern walls may end up, after engineering design, being significantly weaker in flexure than running bond pattern walls. Hence, the primary objective of this study is to investigate the structural behavior of stack pattern and running bond pattern tall masonry walls under constant axial and varying out-of-plane loading. Three running bond patterns and three stack pattern reinforced concrete block masonry walls, each 4.0 m tall ×2.4 m long ×0.19 m thick, were tested under combined out-of-plane bending and axial loading. The test data showed that the failure modes of stack pattern and running bond pattern walls are similar. This study found that the out-of-plane flexural capacity of the stack pattern wall is 8% to 11% lower than the counterpart running bond wall. However, the postcracking behavior of the stack pattern and counterpart running bond walls were found to be similar. Findings from this research suggest that changes to both Canadian Standards Association (CSA) S304 and TMS 402/602 provisions regarding stack pattern masonry are warranted.
See if the study’s test findings would influence your masonry choice in the ASCE Library: https://doi.org/10.1061/JSENDH.STENG-12943.
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